Substrate-less vertical diode integrated circuit structures

ABSTRACT

Substrate-less vertical diode integrated circuit structures, and methods of fabricating substrate-less vertical diode integrated circuit structures, are described. For example, a substrate-less integrated circuit structure includes a semiconductor fin in a dielectric layer, the semiconductor fin having a top and a bottom, and the dielectric layer having a top surface and a bottom surface. A first epitaxial semiconductor structure is on the top of the semiconductor fin. A second epitaxial semiconductor structure is on the bottom of the semiconductor fin. A first conductive contact is on the first epitaxial semiconductor structure. A second conductive contact is on the second epitaxial semiconductor structure.

TECHNICAL FIELD

Embodiments of the disclosure are in the field of integrated circuitstructures and processing and, in particular, substrate-less verticaldiode integrated circuit structures, and methods of fabricatingsubstrate-less vertical diode integrated circuit structures.

BACKGROUND

For the past several decades, the scaling of features in integratedcircuits has been a driving force behind an ever-growing semiconductorindustry. Scaling to smaller and smaller features enables increaseddensities of functional units on the limited real estate ofsemiconductor chips. For example, shrinking transistor size allows forthe incorporation of an increased number of memory or logic devices on achip, lending to the fabrication of products with increased capacity.The drive for ever-more capacity, however, is not without issue. Thenecessity to optimize the performance of each device becomesincreasingly significant.

In the manufacture of integrated circuit devices, multi-gatetransistors, such as tri-gate transistors, have become more prevalent asdevice dimensions continue to scale down. In conventional processes,tri-gate transistors are generally fabricated on either bulk siliconsubstrates or silicon-on-insulator substrates. In some instances, bulksilicon substrates are preferred due to their lower cost and becausethey enable a less complicated tri-gate fabrication process. In anotheraspect, maintaining mobility improvement and short channel control asmicroelectronic device dimensions scale below the 10 nanometer (nm) nodeprovides a challenge in device fabrication.

Scaling multi-gate and nanowire transistors has not been withoutconsequence, however. As the dimensions of these fundamental buildingblocks of microelectronic circuitry are reduced and as the sheer numberof fundamental building blocks fabricated in a given region isincreased, the constraints on the lithographic processes used to patternthese building blocks have become overwhelming. In particular, there maybe a trade-off between the smallest dimension of a feature patterned ina semiconductor stack (the critical dimension) and the spacing betweensuch features.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a cross-sectional view of a substrate-based STIdiode architecture.

FIG. 1B illustrates a cross-sectional view of a substrate-less lateraldiode architecture.

FIG. 1C illustrates a cross-sectional view of a substrate-less diodearchitecture.

FIGS. 2A-2C illustrate cross-sectional views representing variousoperations in a method of fabricating a substrate-less vertical diodearchitecture, in accordance with an embodiment of the presentdisclosure.

FIG. 3 illustrates a cross-sectional view of a non-planar integratedcircuit structure as taken along a gate line, in accordance with anembodiment of the present disclosure.

FIGS. 4A-4H illustrate plan views of a substrate processed withdouble-sided device processing methods, in accordance with someembodiments.

FIGS. 5A-5H illustrate cross-sectional views of a substrate processedwith double-sided device processing methods, in accordance with someembodiments.

FIG. 6 illustrates a cross-sectional view taken through nanowires andfins for a non-endcap architecture, in accordance with an embodiment ofthe present disclosure.

FIG. 7 illustrates a cross-sectional view taken through nanowires andfins for a self-aligned gate endcap (SAGE) architecture, in accordancewith an embodiment of the present disclosure.

FIG. 8A illustrates a three-dimensional cross-sectional view of ananowire-based integrated circuit structure, in accordance with anembodiment of the present disclosure.

FIG. 8B illustrates a cross-sectional source or drain view of thenanowire-based integrated circuit structure of FIG. 8A, as taken alongan a-a′ axis, in accordance with an embodiment of the presentdisclosure.

FIG. 8C illustrates a cross-sectional channel view of the nanowire-basedintegrated circuit structure of FIG. 8A, as taken along the b-b′ axis,in accordance with an embodiment of the present disclosure.

FIG. 9 illustrates a computing device in accordance with oneimplementation of an embodiment of the disclosure.

FIG. 10 illustrates an interposer that includes one or more embodimentsof the disclosure.

DESCRIPTION OF THE EMBODIMENTS

Substrate-less vertical diode integrated circuit structures, and methodsof fabricating substrate-less vertical diode integrated circuitstructures, are described. In the following description, numerousspecific details are set forth, such as specific integration andmaterial regimes, in order to provide a thorough understanding ofembodiments of the present disclosure. It will be apparent to oneskilled in the art that embodiments of the present disclosure may bepracticed without these specific details. In other instances, well-knownfeatures, such as integrated circuit design layouts, are not describedin detail in order to not unnecessarily obscure embodiments of thepresent disclosure. Furthermore, it is to be appreciated that thevarious embodiments shown in the Figures are illustrativerepresentations and are not necessarily drawn to scale.

Certain terminology may also be used in the following description forthe purpose of reference only, and thus are not intended to be limiting.For example, terms such as “upper”, “lower”, “above”, and “below” referto directions in the drawings to which reference is made. Terms such as“front”, “back”, “rear”, and “side” describe the orientation and/orlocation of portions of the component within a consistent but arbitraryframe of reference which is made clear by reference to the text and theassociated drawings describing the component under discussion. Suchterminology may include the words specifically mentioned above,derivatives thereof, and words of similar import.

Embodiments described herein may be directed to front-end-of-line (FEOL)semiconductor processing and structures. FEOL is the first portion ofintegrated circuit (IC) fabrication where the individual devices (e.g.,transistors, capacitors, resistors, etc.) are patterned in thesemiconductor substrate or layer. FEOL generally covers everything up to(but not including) the deposition of metal interconnect layers.Following the last FEOL operation, the result is typically a wafer withisolated transistors (e.g., without any wires).

Embodiments described herein may be directed to back-end of line (BEOL)semiconductor processing and structures. BEOL is the second portion ofIC fabrication where the individual devices (e.g., transistors,capacitors, resistors, etc.) are interconnected with wiring on thewafer, e.g., the metallization layer or layers. BEOL includes contacts,insulating layers (dielectrics), metal levels, and bonding sites forchip-to-package connections. In the BEOL part of the fabrication stagecontacts (pads), interconnect wires, vias and dielectric structures areformed. For modern IC processes, more than 10 metal layers may be addedin the BEOL.

Embodiments described below may be applicable to FEOL processing andstructures, BEOL processing and structures, or both FEOL and BEOLprocessing and structures. In particular, although an exemplaryprocessing scheme may be illustrated using a FEOL processing scenario,such approaches may also be applicable to BEOL processing. Likewise,although an exemplary processing scheme may be illustrated using a BEOLprocessing scenario, such approaches may also be applicable to FEOLprocessing.

One or more embodiments described herein are directed to approaches forfabricating diodes in substrate-less technology, such as a technologyused to enable backside metal interconnects. Embodiments describedherein can be implemented to fabricate vertical diodes, electrostaticdischarge (ESD) diodes, thermal sensors, etc. One or more embodimentsmay be directed to epitaxial (EPI) based Ohmic layers for substrate-lessvertical diodes. One or more embodiments may be directed to approachesfor enhancing lowering contact resistance of Si-backside metal contactsfor turning on diode structures.

To provide context, traditionally low contact resistance between asemiconductor and a metal requires high surface doping in Si, achievedvia in-situ doped EPI and or high dose implant and activation. For abackside interface, a buried layer could be used that suffers fromthermal diffusion and interaction with back-side polish control toensure revealed interface is sufficiently highly doped. Backside-epienables achieving a Si-contact, independent of backside-polish variationand achieve consistently low Si contact resistance. Traditional contactto source/drain is through Epi prior to metal-gate or Cu interconnects.Substrate-less technologies enable access to Front-End from the backsideof the Si-structure. Epi growth technique which functions under exposedmetal and enables a contact from back-side IC, is a strategically novelway to form contacts. Previously there existed a substrate of Si, butnewer technologies are headed towards a substrate-less silicon nanowire(Si-NW) transistors. Thus, a Diode, which relies on presence ofSi-substrate may not be a practical solution. Options withoutSi-substrate are lateral diodes, which are not efficiently workingdevices without a Si-substrate.

To provide further context, all previous diodes rely on a Si-substrate.Vertical diodes need good backside contact and need front-end embeddedEPI layer which are subject thermal-diffusion and will need enoughkeep-away zones to interlayer diffusion. Growth of EPI selectively on Sican lower the barrier potential when a metal makes contact to Si viaEpi-layer. The barrier potential of a metal directly contacting Si, withsmall doping, can lead for a high barrier potential. Introducing an Epilayer between Si and metal can lower that barrier height and thus reducethe contact resistance. In accordance with an embodiment of the presentdisclosure, an Epi layer is introduced between Si and metal enable aback-side metal to form a near-Ohmic contact to Si in a vertical diodearchitecture. Advantages for implementing embodiments described hereincan enable lowering contact resistance for vertical diodes Si-Backsidemetal contact and/or the capability to form controlled interfaces to getlower contact resistance.

Implementation of embodiments described herein can be detected byanalysis of a growth direction which can be detected. The shape of Epigrowth structures can differentiate between growth direction of the epilayer EDX maps can detect type of epi grown. To provide further context,Si as a semiconductor intrinsically has a bandgap and a fermi-level.When a metal is adjacent to Si it forms a Schottky barrier. Lowering thebarrier height will lower the contact resistance between Si and metalwhich needed for any contact resistance. The barrier height is dependenton semiconductor-band gap, metal-type, metal-Si interface and Si dopinglevel. Historically by doping Si the barrier height can be reduced dueto which contact resistance can be lowered. Doping levels needed can behigh around and since the contact was always made on the same side of Siwhich is being doped, there is no risk of amorphization. However, whenthe backside of Si needs an Ohmic contact with a metal, higher dopinglevels risk Si amorphization. Since Epi can be grown selectively on Siand not on a dielectric (such as an oxide) and other surfaces. Doped-Epiand metal can be cleanly achieved without amorphization of Si.

To provide further context, traditional methods to form diode devicesrely on an interdiffused well design in thick a silicon (Si) substrate.Such a design can fail when the Si substrate is removed to facilitatebackside metal interconnects. In accordance with one or more embodimentsof the present disclosure, approaches to enable diodes in asubstrate-less backside interconnect technology are described. Movingfrom a traditional shallow trench isolation (STI) diode to a lateraldiode in substrate-less technology, reverse bias diode leakage canincrease 1000× based on silicon data. A current conduction path instate-of-the-art STI diodes between the Anode to Cathode is under theSTI through the substrate. In lateral diodes, the conduction pathbetween Anode and Cathode is through the channel under the gate, and themain contribution to leakage is off-state subthreshold current.

State-of-the-art solutions for forming diodes in substrate-lesstechnology (e.g., MOBS) can suffer from a fundamental problem that afterSi substrate removal, the resulting Si body is thin which reducescurrent carrying capacity of the diodes. In such cases, fin height needsto be made taller to increase Si body, which can lead to fin stabilityconcerns.

As a comparative example, FIG. 1A illustrates a cross-sectional view ofa substrate-based STI diode architecture. Referring to FIG. 1A, anintegrated circuit structure 100 includes a fin 108 on a substrate 102,such as a silicon fin on a silicon substrate. The substrate 102 includesa P-doped substrate portion 104 and an NWELL substrate portion 106. Thefin 108 can include the NWELL doping. The height of fin 108 is shown as110. A plurality of gate structures 112 includes gate caps 112A on gateportions 112B. P-type epitaxial (Epi) structures 116, such asboron-doped silicon or boron-doped silicon germanium structures, arebetween adjacent ones of the plurality of gate structures 112. Aplurality of gate structures 114 includes gate caps 114A on gateportions 114B. N-type epitaxial (Epi) structures 118, such asphosphorous-doped silicon structures, are between adjacent ones of theplurality of gate structures 114. A diode 120 incudes one of the P-typeepitaxial (Epi) structures 116 and one of N-type epitaxial (Epi)structures 118 with a pathway that is through the substrate 102.

As an exemplary lateral diode architecture, FIG. 1B illustrates across-sectional view of a substrate-less lateral diode architecture, inaccordance with another embodiment of the present disclosure. Referringto FIG. 1B, an integrated circuit structure 130 includes a fin 132, suchas a silicon fin. The fin 132 can include an N-diffusion region 134 inan otherwise P-diffusion fin. A plurality of gate structures 136includes gate caps 136A on gate portions 136B. P-type epitaxial (Epi)structures 138, such as boron-doped silicon or boron-doped silicongermanium structures, and N-type epitaxial (Epi) structures 140, such asphosphorous-doped silicon structures, are between select ones of theplurality of gate structures 136. Contacts 142 and 144 may be formed onthe P-type epitaxial (Epi) structures 138 and N-type epitaxial (Epi)structures 140, respectively. A diode incudes one of the P-typeepitaxial (Epi) structures 138 and one of N-type epitaxial (Epi)structures 140 with a pathway that is through the fin 132. In oneembodiment, since the pathway does not require a bulk substrate, thediode functions on a substrate-less architecture, e.g., where a bulksubstrate has been removed from fin 132.

As an example of a vertical diode without a backside epitaxialstructure, FIG. 1C illustrates a cross-sectional view of asubstrate-less diode architecture.

Referring to FIG. 1C, an integrated circuit structure 150 includes fins152. Each fin 152 has a lower P-type portion 154 and an upper N-typeportion 156. The integrated circuit structure 150 can further includeN-type epitaxial structures 158 on the fins 152, and a conductivecontact structure 160 on the N-type epitaxial structures 158. The fins152 can be included in a dielectric layer 162, as is depicted. Aconductive contact 166 is on the backside of the dielectric layer 162and makes electrical contact to the fins 152 from the backside. It is tobe appreciated that since a bulk substrate has been removed, an ESDdiode fabricated from the structure can exhibit relatively increasedcontact resistance, especially at the backside contact.

As an exemplary processing scheme for fabricating a backside epitaxialstructure for a diode, FIGS. 2A-2C illustrate cross-sectional viewsrepresenting various operations in a method of fabricating asubstrate-less vertical diode architecture, in accordance with anembodiment of the present disclosure.

Referring to FIG. 2A, a starting structure 200 includes a plurality offins 204 extending from a substrate 202. The plurality of fins 204 isincluded in a dielectric layer 206. Epitaxial semiconductor structures208 are formed at the tops of the plurality of fins 204, e.g., onsurfaces of the plurality of fins 204 recessed, and possibly faceted, byan etch process. A metal contact 210 is over the epitaxial semiconductorstructures 208.

Referring to FIG. 2B, the substrate 202 is removed from the backside inorder to form a substrate-less structure, e.g., for backside contactaccess. Removal of the substrate 202 reveals a backside of the pluralityof fins 204. In one embodiment, the patterned substrate 202 is removedby a post backside polish process, described in greater detail below.

Referring to FIG. 2C, the backside of the plurality of fins 204 may besubjected to a recess etch which may facet the backside surfaces of theplurality of fins 204, forming etched fins 204A of an integrated circuitstructure 250. Subsequently, backside epitaxial semiconductor structures212 are formed on the backside of the fins 204A. A backside contact 212can then be formed on the backside epitaxial semiconductor structures212.

With reference again to FIG. 2C, in accordance with an embodiment of thepresent disclosure, a substrate-less integrated circuit structure 250includes a semiconductor fin 204A in a dielectric layer 206. Thesemiconductor fin 204A has a top and a bottom, and the dielectric layer206 has a top surface and a bottom surface. A first epitaxialsemiconductor structure 208 is on the top of the semiconductor fin 204A.A second epitaxial semiconductor structure 212 is on the bottom of thesemiconductor fin 204A. A first conductive contact 210 is on the firstepitaxial semiconductor structure 208. A second conductive contact 214is on the second epitaxial semiconductor structure 212.

In one embodiment, the first epitaxial semiconductor structure 208 has abottom below the top surface of the dielectric layer 206, and the secondepitaxial semiconductor structure 212 has a top above the bottom surfaceof the dielectric layer 206. In one embodiment, the fin 204A includessilicon, and the first 208 and second 212 epitaxial semiconductorstructures include silicon and germanium. In one embodiment, the first208 and second 212 epitaxial semiconductor structures are faceted, as isdepicted. In one embodiment, the integrated circuit structure 250 is avertical diode.

With reference again to FIG. 2C, in accordance with another embodimentof the present disclosure, a substrate-less integrated circuit structure250 includes a plurality of fins 204A in a dielectric layer 206. Aplurality of N-type epitaxial structures 208 is on a top of theplurality of fins 204A. A plurality of P-type epitaxial structures 212is on a bottom of the plurality of fins 204A. A first conductive contact210 is on the plurality of N-type epitaxial structures 208. A secondconductive contact 214 is on the plurality of P-type epitaxialstructures 212.

In one embodiment, the plurality of fins 204A is a plurality of N-typefins. In another embodiment, the plurality of fins 204A is a pluralityof P-type fins. In one embodiment, the plurality of fins 204A includessilicon, the plurality of N-type epitaxial structures 208 includessilicon and germanium, and the plurality of P-type epitaxial structures212 includes silicon and germanium. In one embodiment, the integratedcircuit structure 250 is a vertical diode.

It is to be appreciated that, as used throughout the disclosure, a fin,a lower fin portion, an upper fin portion, a nanowire, a nanoribbon, oran epitaxial structure may be or may include a silicon layer. A siliconlayer may be used to describe a silicon material composed of a verysubstantial amount of, if not all, silicon. However, it is to beappreciated that, practically, 100% pure Si may be difficult to formand, hence, could include a tiny percentage of carbon, germanium or tin.Such impurities may be included as an unavoidable impurity or componentduring deposition of Si or may “contaminate” the Si upon diffusionduring post deposition processing. As such, embodiments described hereindirected to a silicon layer may include a silicon layer that contains arelatively small amount, e.g., “impurity” level, non-Si atoms orspecies, such as Ge, C or Sn. It is to be appreciated that a siliconlayer as described herein may be undoped or may be doped with dopantatoms such as boron, phosphorous or arsenic.

It is to be appreciated that, as used throughout the disclosure, a fin,a lower fin portion, an upper fin portion, a nanowire, a nanoribbon, oran epitaxial structure may be or may include a silicon germanium layer.A silicon germanium layer may be used to describe a silicon materialcomposed of substantial portions of both silicon and germanium, such asat least 5% of both. In some embodiments, the amount of germanium isgreater than the amount of silicon. In particular embodiments, a silicongermanium layer includes approximately 60% germanium and approximately40% silicon (Si₄₀Ge₆₀). In other embodiments, the amount of silicon isgreater than the amount of germanium. In particular embodiments, asilicon germanium layer includes approximately 30% germanium andapproximately 70% silicon (Si₇₀Ge₃₀). It is to be appreciated that,practically, 100% pure silicon germanium (referred to generally as SiGe)may be difficult to form and, hence, could include a tiny percentage ofcarbon or tin. Such impurities may be included as an unavoidableimpurity or component during deposition of SiGe or may “contaminate” theSiGe upon diffusion during post deposition processing. As such,embodiments described herein directed to a silicon germanium layer mayinclude a silicon germanium layer that contains a relatively smallamount, e.g., “impurity” level, non-Ge and non-Si atoms or species, suchas carbon or tin. It is to be appreciated that a silicon germanium layeras described herein may be undoped or may be doped with dopant atomssuch as boron, phosphorous or arsenic.

It is to be appreciated that the vertical diode structures describedabove in association with FIG. 2C can be co-integrated with othersubstrate-less integrated circuit structures. Alternatively, oradditionally, other types of substrate-less integrated circuitstructures may be fabricated to include backside epitaxial semiconductorstructures. As an example of a substrate-less device for co-integrationor for inclusion of backside epitaxial semiconductor structures, FIG. 3illustrate a cross-sectional view of a non-planar integrated circuitstructure as taken along a gate line, in accordance with an embodimentof the present disclosure.

Referring to FIG. 3, a semiconductor structure or device 300 includes anon-planar active region (e.g., a fin structure including protruding finportion 304 and sub-fin region 305) within a trench isolation region306. In an embodiment, instead of a solid fin, the non-planar activeregion is separated into nanowires (such as nanowires 304A and 304B)above sub-fin region 305, as is represented by the dashed lines. Ineither case, for ease of description for non-planar integrated circuitstructure 300, a non-planar active region 304 is referenced below as aprotruding fin portion. It is to be appreciated that, in one embodiment,there is no bulk substrate coupled to the sub-fin region 305.

A gate line 308 is disposed over the protruding portions 304 of thenon-planar active region (including, if applicable, surroundingnanowires 304A and 304B), as well as over a portion of the trenchisolation region 306. As shown, gate line 308 includes a gate electrode350 and a gate dielectric layer 352. In one embodiment, gate line 308may also include a dielectric cap layer 354. A gate contact 314, andoverlying gate contact via 316 are also seen from this perspective,along with an overlying metal interconnect 360, all of which aredisposed in inter-layer dielectric stacks or layers 370. Also seen fromthe perspective of FIG. 3, the gate contact 314 is, in one embodiment,disposed over trench isolation region 306, but not over the non-planaractive regions.

In an embodiment, the semiconductor structure or device 300 is anon-planar device such as, but not limited to, a fin-FET device, atri-gate device, a nano-ribbon device, or a nano-wire device. In such anembodiment, a corresponding semiconducting channel region is composed ofor is formed in a three-dimensional body. In one such embodiment, thegate electrode stacks of gate lines 308 surround at least a top surfaceand a pair of sidewalls of the three-dimensional body.

As is also depicted in FIG. 3, in an embodiment, an interface 380 existsbetween a protruding fin portion 304 and sub-fin region 305. Theinterface 380 can be a transition region between a doped sub-fin region305 and a lightly or undoped upper fin portion 304. In one suchembodiment, each fin is approximately 10 nanometers wide or less, andsub-fin dopants are supplied from an adjacent solid state doping layerat the sub-fin location. In a particular such embodiment, each fin isless than 10 nanometers wide. In another embodiment, the subfin regionis a dielectric material, formed by recessing the fin through a wet ordry etch, and filling the recessed cavity with a conformal or flowabledielectric.

Although not depicted in FIG. 3, it is to be appreciated that source ordrain regions of or adjacent to the protruding fin portions 304 are oneither side of the gate line 308, i.e., into and out of the page. In oneembodiment, the source or drain regions are doped portions of originalmaterial of the protruding fin portions 304. In another embodiment, thematerial of the protruding fin portions 304 is removed and replaced withanother semiconductor material, e.g., by epitaxial deposition to formdiscrete epitaxial nubs or non-discrete epitaxial structures. In eitherembodiment, the source or drain regions may extend below the height ofdielectric layer of trench isolation region 306, i.e., into the sub-finregion 305. In accordance with an embodiment of the present disclosure,the more heavily doped sub-fin regions, i.e., the doped portions of thefins below interface 380, inhibits source to drain leakage through thisportion of the bulk semiconductor fins.

With reference again to FIG. 3, in an embodiment, fins 304/305 (and,possibly nanowires 304A and 304B) are composed of a crystalline silicon,silicon/germanium or germanium layer doped with a charge carrier, suchas but not limited to phosphorus, arsenic, boron or a combinationthereof. In one embodiment, the concentration of silicon atoms isgreater than 93%. In another embodiment, fins 304/305 are composed of agroup III-V material, such as, but not limited to, gallium nitride,gallium phosphide, gallium arsenide, indium phosphide, indiumantimonide, indium gallium arsenide, aluminum gallium arsenide, indiumgallium phosphide, or a combination thereof. Trench isolation region 306may be composed of a dielectric material such as, but not limited to,silicon dioxide, silicon oxy-nitride, silicon nitride, or carbon-dopedsilicon nitride.

Gate line 308 may be composed of a gate electrode stack which includes agate dielectric layer 352 and a gate electrode layer 350. In anembodiment, the gate electrode of the gate electrode stack is composedof a metal gate and the gate dielectric layer is composed of a high-kmaterial. For example, in one embodiment, the gate dielectric layer iscomposed of a material such as, but not limited to, hafnium oxide,hafnium oxy-nitride, hafnium silicate, lanthanum oxide, zirconium oxide,zirconium silicate, tantalum oxide, barium strontium titanate, bariumtitanate, strontium titanate, yttrium oxide, aluminum oxide, leadscandium tantalum oxide, lead zinc niobate, or a combination thereof.Furthermore, a portion of gate dielectric layer may include a layer ofnative oxide formed from the top few layers of the substrate fin 304. Inan embodiment, the gate dielectric layer is composed of a top high-kportion and a lower portion composed of an oxide of a semiconductormaterial. In one embodiment, the gate dielectric layer is composed of atop portion of hafnium oxide and a bottom portion of silicon dioxide orsilicon oxy-nitride. In some implementations, a portion of the gatedielectric is a “U”-shaped structure that includes a bottom portionsubstantially parallel to the surface of the substrate and two sidewallportions that are substantially perpendicular to the top surface of thesubstrate.

In one embodiment, the gate electrode is composed of a metal layer suchas, but not limited to, metal nitrides, metal carbides, metal silicides,metal aluminides, hafnium, zirconium, titanium, tantalum, aluminum,ruthenium, palladium, platinum, cobalt, nickel or conductive metaloxides. In a specific embodiment, the gate electrode is composed of anon-workfunction-setting fill material formed above a metalworkfunction-setting layer. The gate electrode layer may consist of aP-type workfunction metal or an N-type workfunction metal, depending onwhether the transistor is to be a PMOS or an NMOS transistor. In someimplementations, the gate electrode layer may consist of a stack of twoor more metal layers, where one or more metal layers are workfunctionmetal layers and at least one metal layer is a conductive fill layer.For a PMOS transistor, metals that may be used for the gate electrodeinclude, but are not limited to, ruthenium, palladium, platinum, cobalt,nickel, and conductive metal oxides, e.g., ruthenium oxide. A P-typemetal layer will enable the formation of a PMOS gate electrode with aworkfunction that is between about 4.9 eV and about 5.2 eV. For an NMOStransistor, metals that may be used for the gate electrode include, butare not limited to, hafnium, zirconium, titanium, tantalum, aluminum,alloys of these metals, and carbides of these metals such as hafniumcarbide, zirconium carbide, titanium carbide, tantalum carbide, andaluminum carbide. An N-type metal layer will enable the formation of anNMOS gate electrode with a workfunction that is between about 3.9 eV andabout 4.2 eV. In some implementations, the gate electrode may consist ofa “U”-shaped structure that includes a bottom portion substantiallyparallel to the surface of the substrate and two sidewall portions thatare substantially perpendicular to the top surface of the substrate. Inanother implementation, at least one of the metal layers that form thegate electrode may simply be a planar layer that is substantiallyparallel to the top surface of the substrate and does not includesidewall portions substantially perpendicular to the top surface of thesubstrate. In further implementations of the disclosure, the gateelectrode may consist of a combination of U-shaped structures andplanar, non-U-shaped structures. For example, the gate electrode mayconsist of one or more U-shaped metal layers formed atop one or moreplanar, non-U-shaped layers.

Spacers associated with the gate electrode stacks may be composed of amaterial suitable to ultimately electrically isolate, or contribute tothe isolation of, a permanent gate structure from adjacent conductivecontacts, such as self-aligned contacts. For example, in one embodiment,the spacers are composed of a dielectric material such as, but notlimited to, silicon dioxide, silicon oxy-nitride, silicon nitride, orcarbon-doped silicon nitride.

Gate contact 314 and overlying gate contact via 316 may be composed of aconductive material. In an embodiment, one or more of the contacts orvias are composed of a metal species. The metal species may be a puremetal, such as tungsten, nickel, or cobalt, or may be an alloy such as ametal-metal alloy or a metal-semiconductor alloy (e.g., such as asilicide material).

In an embodiment (although not shown), a contact pattern which isessentially perfectly aligned to an existing gate pattern 308 is formedwhile eliminating the use of a lithographic step with exceedingly tightregistration budget. In one such embodiment, the self-aligned approachenables the use of intrinsically highly selective wet etching (e.g.,versus conventionally implemented dry or plasma etching) to generatecontact openings. In an embodiment, a contact pattern is formed byutilizing an existing gate pattern in combination with a contact pluglithography operation. In one such embodiment, the approach enableselimination of the need for an otherwise critical lithography operationto generate a contact pattern, as used in conventional approaches. In anembodiment, a trench contact grid is not separately patterned, but israther formed between poly (gate) lines. For example, in one suchembodiment, a trench contact grid is formed subsequent to gate gratingpatterning but prior to gate grating cuts.

In an embodiment, providing structure 300 involves fabrication of thegate stack structure 308 by a replacement gate process. In such ascheme, dummy gate material such as polysilicon or silicon nitridepillar material, may be removed and replaced with permanent gateelectrode material. In one such embodiment, a permanent gate dielectriclayer is also formed in this process, as opposed to being carriedthrough from earlier processing. In an embodiment, dummy gates areremoved by a dry etch or wet etch process. In one embodiment, dummygates are composed of polycrystalline silicon or amorphous silicon andare removed with a dry etch process including use of SF₆. In anotherembodiment, dummy gates are composed of polycrystalline silicon oramorphous silicon and are removed with a wet etch process including useof aqueous NH₄OH or tetramethylammonium hydroxide. In one embodiment,dummy gates are composed of silicon nitride and are removed with a wetetch including aqueous phosphoric acid.

Referring again to FIG. 3, the arrangement of semiconductor structure ordevice 300 places the gate contact over isolation regions. Such anarrangement may be viewed as inefficient use of layout space. In anotherembodiment, however, a semiconductor device has contact structures thatcontact portions of a gate electrode formed over an active region, e.g.,over a sub-fin 305, and in a same layer as a trench contact via.

It is to be appreciated that not all aspects of the processes describedabove need be practiced to fall within the spirit and scope ofembodiments of the present disclosure. For example, in one embodiment,dummy gates need not ever be formed prior to fabricating gate contactsover active portions of the gate stacks. The gate stacks described abovemay actually be permanent gate stacks as initially formed. Also, theprocesses described herein may be used to fabricate one or a pluralityof semiconductor devices. The semiconductor devices may be transistorsor like devices. For example, in an embodiment, the semiconductordevices are a metal-oxide semiconductor (MOS) transistors for logic ormemory, or are bipolar transistors. Also, in an embodiment, thesemiconductor devices have a three-dimensional architecture, such as atrigate device, an independently accessed double gate device, or aFIN-FET. One or more embodiments may be particularly useful forfabricating semiconductor devices at a sub-10 nanometer (10 nm)technology node.

In an embodiment, as used throughout the present description, interlayerdielectric (ILD) material is composed of or includes a layer of adielectric or insulating material. Examples of suitable dielectricmaterials include, but are not limited to, oxides of silicon (e.g.,silicon dioxide (SiO₂)), doped oxides of silicon, fluorinated oxides ofsilicon, carbon doped oxides of silicon, various low-k dielectricmaterials known in the arts, and combinations thereof. The interlayerdielectric material may be formed by conventional techniques, such as,for example, chemical vapor deposition (CVD), physical vapor deposition(PVD), or by other deposition methods.

In an embodiment, as is also used throughout the present description,metal lines or interconnect line material (and via material) is composedof one or more metal or other conductive structures. A common example isthe use of copper lines and structures that may or may not includebarrier layers between the copper and surrounding ILD material. As usedherein, the term metal includes alloys, stacks, and other combinationsof multiple metals. For example, the metal interconnect lines mayinclude barrier layers (e.g., layers including one or more of Ta, TaN,Ti or TiN), stacks of different metals or alloys, etc. Thus, theinterconnect lines may be a single material layer, or may be formed fromseveral layers, including conductive liner layers and fill layers. Anysuitable deposition process, such as electroplating, chemical vapordeposition or physical vapor deposition, may be used to forminterconnect lines. In an embodiment, the interconnect lines arecomposed of a conductive material such as, but not limited to, Cu, Al,Ti, Zr, Hf, V, Ru, Co, Ni, Pd, Pt, W, Ag, Au or alloys thereof. Theinterconnect lines are also sometimes referred to in the art as traces,wires, lines, metal, or simply interconnect.

In an embodiment, as is also used throughout the present description,hardmask materials, capping layers, or plugs are composed of dielectricmaterials different from the interlayer dielectric material. In oneembodiment, different hardmask, capping or plug materials may be used indifferent regions so as to provide different growth or etch selectivityto each other and to the underlying dielectric and metal layers. In someembodiments, a hardmask layer, capping or plug layer includes a layer ofa nitride of silicon (e.g., silicon nitride) or a layer of an oxide ofsilicon, or both, or a combination thereof. Other suitable materials mayinclude carbon-based materials. Other hardmask, capping or plug layersknown in the arts may be used depending upon the particularimplementation. The hardmask, capping or plug layers maybe formed byCVD, PVD, or by other deposition methods.

In an embodiment, as is also used throughout the present description,lithographic operations are performed using 193 nm immersion lithography(i193), EUV and/or EBDW lithography, or the like. A positive tone or anegative tone resist may be used. In one embodiment, a lithographic maskis a trilayer mask composed of a topographic masking portion, ananti-reflective coating (ARC) layer, and a photoresist layer. In aparticular such embodiment, the topographic masking portion is a carbonhardmask (CHM) layer and the anti-reflective coating layer is a siliconARC layer.

In another aspect, integrated circuit structures described herein may befabricated using a back-side reveal of front-side structures fabricationapproach. In some exemplary embodiments, reveal of the back-side of atransistor or other device structure entails wafer-level back-sideprocessing. In contrast to a conventional TSV-type technology, a revealof the back-side of a transistor as described herein may be performed atthe density of the device cells, and even within sub-regions of adevice. Furthermore, such a reveal of the back-side of a transistor maybe performed to remove substantially all of a donor substrate upon whicha device layer was disposed during front-side device processing. Assuch, a microns-deep TSV becomes unnecessary with the thickness ofsemiconductor in the device cells following a reveal of the back-side ofa transistor potentially being only tens or hundreds of nanometers.

Reveal techniques described herein may enable a paradigm shift from“bottom-up” device fabrication to “center-out” fabrication, where the“center” is any layer that is employed in front-side fabrication,revealed from the back side, and again employed in back-sidefabrication. Processing of both a front side and revealed back side of adevice structure may address many of the challenges associated withfabricating 3D ICs when primarily relying on front-side processing.

A reveal of the back-side of a transistor approach may be employed forexample to remove at least a portion of a carrier layer and interveninglayer of a donor-host substrate assembly, for example as illustrated inFIGS. 4A-4H and 5A-5H, described below. The process flow begins with aninput of a donor-host substrate assembly. A thickness of a carrier layerin the donor-host substrate is polished (e.g., CMP) and/or etched with awet or dry (e.g., plasma) etch process. Any grind, polish, and/orwet/dry etch process known to be suitable for the composition of thecarrier layer may be employed. For example, where the carrier layer is agroup IV semiconductor (e.g., silicon) a CMP slurry known to be suitablefor thinning the semiconductor may be employed. Likewise, any wetetchant or plasma etch process known to be suitable for thinning thegroup IV semiconductor may also be employed.

In some embodiments, the above is preceded by cleaving the carrier layeralong a fracture plane substantially parallel to the intervening layer.The cleaving or fracture process may be utilized to remove a substantialportion of the carrier layer as a bulk mass, reducing the polish or etchtime needed to remove the carrier layer. For example, where a carrierlayer is 400-900 μm in thickness, 100-700 μm may be cleaved off bypracticing any blanket implant known to promote a wafer-level fracture.In some exemplary embodiments, a light element (e.g., H, He, or Li) isimplanted to a uniform target depth within the carrier layer where thefracture plane is desired. Following such a cleaving process, thethickness of the carrier layer remaining in the donor-host substrateassembly may then be polished or etched to complete removal.Alternatively, where the carrier layer is not fractured, the grind,polish and/or etch operation may be employed to remove a greaterthickness of the carrier layer.

Next, exposure of an intervening layer is detected. Detection is used toidentify a point when the back-side surface of the donor substrate hasadvanced to nearly the device layer. Any endpoint detection techniqueknown to be suitable for detecting a transition between the materialsemployed for the carrier layer and the intervening layer may bepracticed. In some embodiments, one or more endpoint criteria are basedon detecting a change in optical absorbance or emission of the back-sidesurface of the donor substrate during the polishing or etchingperformed. In some other embodiments, the endpoint criteria areassociated with a change in optical absorbance or emission of byproductsduring the polishing or etching of the donor substrate back-sidesurface. For example, absorbance or emission wavelengths associated withthe carrier layer etch byproducts may change as a function of thedifferent compositions of the carrier layer and intervening layer. Inother embodiments, the endpoint criteria are associated with a change inmass of species in byproducts of polishing or etching the back-sidesurface of the donor substrate. For example, the byproducts ofprocessing may be sampled through a quadrupole mass analyzer and achange in the species mass may be correlated to the differentcompositions of the carrier layer and intervening layer. In anotherexemplary embodiment, the endpoint criteria is associated with a changein friction between a back-side surface of the donor substrate and apolishing surface in contact with the back-side surface of the donorsubstrate.

Detection of the intervening layer may be enhanced where the removalprocess is selective to the carrier layer relative to the interveninglayer as non-uniformity in the carrier removal process may be mitigatedby an etch rate delta between the carrier layer and intervening layer.Detection may even be skipped if the grind, polish and/or etch operationremoves the intervening layer at a rate sufficiently below the rate atwhich the carrier layer is removed. If an endpoint criteria is notemployed, a grind, polish and/or etch operation of a predetermined fixedduration may stop on the intervening layer material if the thickness ofthe intervening layer is sufficient for the selectivity of the etch. Insome examples, the carrier etch rate:intervening layer etch rate is3:1-10:1, or more.

Upon exposing the intervening layer, at least a portion of theintervening layer may be removed. For example, one or more componentlayers of the intervening layer may be removed. A thickness of theintervening layer may be removed uniformly by a polish, for example.Alternatively, a thickness of the intervening layer may be removed witha masked or blanket etch process. The process may employ the same polishor etch process as that employed to thin the carrier, or may be adistinct process with distinct process parameters. For example, wherethe intervening layer provides an etch stop for the carrier removalprocess, the latter operation may employ a different polish or etchprocess that favors removal of the intervening layer over removal of thedevice layer. Where less than a few hundred nanometers of interveninglayer thickness is to be removed, the removal process may be relativelyslow, optimized for across-wafer uniformity, and more preciselycontrolled than that employed for removal of the carrier layer. A CHIPprocess employed may, for example employ a slurry that offers very highselectively (e.g., 100:1-300:1, or more) between semiconductor (e.g.,silicon) and dielectric material (e.g., SiO) surrounding the devicelayer and embedded within the intervening layer, for example, aselectrical isolation between adjacent device regions.

For embodiments where the device layer is revealed through completeremoval of the intervening layer, backside processing may commence on anexposed backside of the device layer or specific device regions therein. In some embodiments, the backside device layer processing includes afurther polish or wet/dry etch through a thickness of the device layerdisposed between the intervening layer and a device region previouslyfabricated in the device layer, such as a source or drain region.

In some embodiments where the carrier layer, intervening layer, ordevice layer backside is recessed with a wet and/or plasma etch, such anetch may be a patterned etch or a materially selective etch that impartssignificant non-planarity or topography into the device layer back-sidesurface. As described further below, the patterning may be within adevice cell (i.e., “intra-cell” patterning) or may be across devicecells (i.e., “inter-cell” patterning). In some patterned etchembodiments, at least a partial thickness of the intervening layer isemployed as a hard mask for back-side device layer patterning. Hence, amasked etch process may preface a correspondingly masked device layeretch.

The above described processing scheme may result in a donor-hostsubstrate assembly that includes IC devices that have a back side of anintervening layer, a back side of the device layer, and/or back side ofone or more semiconductor regions within the device layer, and/orfront-side metallization revealed. Additional backside processing of anyof these revealed regions may then be performed during downstreamprocessing.

In accordance with one or more embodiments of the present disclosure, inorder to enable backside access to a partitioned source or drain contactstructure, a double-sided device processing scheme may be practiced atthe wafer-level. In some exemplary embodiments, a large formal substrate(e.g., 300 or 450 mm diameter) wafer may be processed. In an exemplaryprocessing scheme, a donor substrate including a device layer isprovided. In some embodiments, the device layer is a semiconductormaterial that is employed by an IC device. As one example, in atransistor device, such as a field effect transistor (FET), the channelsemiconductor is formed from the semiconductor device layer. As anotherexample, for an optical device, such as a photodiode, the drift and/orgain semiconductor is formed from the device layer. The device layer mayalso be employed in a passive structure with an IC device. For example,an optical waveguide may employ semiconductor patterned from the devicelayer.

In some embodiments, the donor substrate includes a stack of materiallayers. Such a material stack may facilitate subsequent formation of anIC device stratum that includes the device layer but lacks other layersof the donor substrate. In an exemplary embodiment, the donor substrateincludes a carrier layer separated from the device layer by one or moreintervening material layers. The carrier layer is to provide mechanicalsupport during front-side processing of the device layer. The carriermay also provide the basis for crystallinity in the semiconductor devicelayer. The intervening layer(s) may facilitate removal of the carrierlayer and/or the reveal of the device layer backside.

Front-side fabrication operations are then performed to form a devicestructure that includes one or more regions in the device layer. Anyknown front-side processing techniques may be employed to form any knownIC device and exemplary embodiments are further described elsewhereherein. A front side of the donor substrate is then joined to a hostsubstrate to form a device-host assembly. The host substrate is toprovide front-side mechanical support during back-side processing of thedevice layer. The host substrate may also entail integrated circuitrywith which the IC devices fabricated on the donor substrate areinterconnected. For such embodiments, joining of the host and donorsubstrate may further entail formation of 3D interconnect structuresthrough hybrid (dielectric/metal) bonding. Any known host substrate andwafer-level joining techniques may be employed.

The process flow continues where the back side of the device stratum isrevealed by removing at least a portion of the carrier layer. In somefurther embodiments, portions of any intervening layer and/or front-sidematerials deposited over the device layer may also be removed during thereveal operation. As described elsewhere herein in the context of someexemplary embodiments, an intervening layer(s) may facilitate ahighly-uniform exposure of the device stratum back-side, for exampleserving as one or more of an etch marker or etch stop employed in thewafer-level backside reveal process. Device stratum surfaces exposedfrom the back side are processed to form a double-side device stratum.Native materials, such as any of those of the donor substrate, whichinterfaced with the device regions may then be replaced with one or morenon-native materials. For example, a portion of a semiconductor devicelayer or intervening layer may be replaced with one or more othersemiconductor, metal, or dielectric materials. In some furtherembodiments, portions of the front-side materials removed during thereveal operation may also be replaced. For example, a portion of adielectric spacer, gate stack, or contact metallization formed duringfront-side device fabrication may be replaced with one or more othersemiconductor, metal, or dielectric materials during backsidedeprocessing/reprocessing of the front-side device. In still otherembodiments, a second device stratum or metal interposer is bonded tothe reveal back-side.

The above process flow provides a device stratum-host substrateassembly. The device stratum-host assembly may then be furtherprocessed. For example, any known technique may be employed to singulateand package the device stratum-host substrate assembly. Where the hostsubstrate is entirely sacrificial, packaging of the device stratum-hostsubstrate may entail separation of the host substrate from the devicestratum. Where the host substrate is not entirely sacrificial (e.g.,where the host substrate also includes a device stratum), the devicestratum-host assembly output may be fed back as a host substrate inputduring a subsequent iteration of the above process flow. Iteration ofthe above approach may thus form a wafer-level assembly of any number ofdouble-side device strata, each only tens or hundreds of nanometers inthickness, for example. In some embodiments, and as further describedelsewhere herein, one or more device cells within a device stratum areelectrically tested, for example as a yield control point in thefabrication of a wafer-level assembly of double-side device strata. Insome embodiments, the electrical test entails back-side device probing.

FIGS. 4A-4H illustrate plan views of a substrate processed withdouble-sided device processing methods, in accordance with someembodiments. FIGS. 5A-5H illustrate cross-sectional views of a substrateprocessed with double-sided device processing methods, in accordancewith some embodiments.

As shown in FIGS. 4A and 5A, donor substrate 401 includes a plurality ofIC die 411 in an arbitrary spatial layout over a front-side wafersurface. Front-side processing of IC die 411 may have been performedfollowing any techniques to form any device structures. In exemplaryembodiments, die 411 include one or more semiconductor regions withindevice layer 415. An intervening layer 410 separates device layer 415from carrier layer 405. In the exemplary embodiment, intervening layer410 is in direct contact with both carrier layer 405 and device layer415. Alternatively, one or more spacer layers may be disposed betweenintervening layer 410 and device layer 415 and/or carrier layer 405.Donor substrate 401 may further include other layers, for exampledisposed over device layer 415 and/or below carrier layer 405.

Device layer 415 may include one or more layers of any device materialcomposition known to be suitable for a particular IC device, such as,but not limited to, transistors, diodes, and resistors. In someexemplary embodiments, device layer 415 includes one or more group IV(i.e., IUPAC group 14) semiconductor material layers (e.g., Si, Ge,SiGe), group III-V semiconductor material layers (e.g., GaAs, InGaAs,InAs, InP), or group III-N semiconductor material layers (e.g., GaN,AlGaN, InGaN). Device layer 415 may also include one or moresemiconductor transition metal dichalcogenide (TMD or TMDC) layers. Inother embodiments, device layer 415 includes one or more graphene layer,or a graphenic material layer having semiconductor properties. In stillother embodiments, device layer 415 includes one or more oxidesemiconductor layers. Exemplary oxide semiconductors include oxides of atransition metal (e.g., IUPAC group 4-10) or post-transition metal(e.g., IUPAC groups 11-14). In advantageous embodiments, the oxidesemiconductor includes at least one of Cu, Zn, Sn, Ti, Ni, Ga, In, Sr,Cr, Co, V, or Mo. The metal oxides may be suboxides (A₂O) monoxides(AO), binary oxides (AO₂), ternary oxides (ABO₃), and mixtures thereof.In other embodiments, device layer 415 includes one or more magnetic,ferromagnetic, ferroelectric material layer. For example device layer415 may include one or more layers of any material known to be suitablefor an tunneling junction device, such as, but not limited to a magnetictunneling junction (MTJ) device.

In some embodiments, device layer 415 is substantially monocrystalline.Although monocrystalline, a significant number of crystalline defectsmay nonetheless be present. In other embodiments, device layer 415 isamorphous or nanocrystalline. Device layer 415 may be any thickness(e.g., z-dimension in FIG. 5A). In some exemplary embodiments, devicelayer 415 has a thickness greater than a z-thickness of at least some ofthe semiconductor regions employed by die 411 as functionalsemiconductor regions of die 411 built on and/or embedded within devicelayer 415 need not extend through the entire thickness of device layer415. In some embodiments, semiconductor regions of die 411 are disposedonly within a top-side thickness of device layer 415 demarked in FIG. 5Aby dashed line 412. For example, semiconductor regions of die 411 mayhave a z-thickness of 200-300 nm, or less, while device layer may have az-thickness of 700-1000 nm, or more. As such, around 600 nm of devicelayer thickness may separate semiconductor regions of die 411 fromintervening layer 410.

Carrier layer 405 may have the same material composition as device layer415, or may have a material composition different than device layer 415.For embodiments where carrier layer 405 and device layer 415 have thesame composition, the two layers may be identified by their positionrelative to intervening layer 410. In some embodiments where devicelayer 415 is a crystalline group IV, group III-V or group III-Nsemiconductor, carrier layer 405 is the same crystalline group IV, groupIII-V or group III-N semiconductor as device layer 415. In alternativeembodiments, where device layer 415 is a crystalline group IV, groupIII-V or group III-N semiconductor, carrier layer 405 is a differentcrystalline group IV, group III-V or group III-N semiconductor thandevice layer 415. In still other embodiments, carrier layer 405 mayinclude, or be, a material onto which device layer 415 transferred, orgrown upon. For example, carrier layer may include one or more amorphousoxide layers (e.g., glass) or crystalline oxide layer (e.g., sapphire),polymer sheets, or any material(s) built up or laminated into astructural support known to be suitable as a carrier during IC deviceprocessing. Carrier layer 405 may be any thickness (e.g., z-dimension inFIG. 5A) as a function of the carrier material properties and thesubstrate diameter. For example, where the carrier layer 405 is a largeformat (e.g., 300-450 mm) semiconductor substrate, the carrier layerthickness may be 700-1000 or more.

In some embodiments, one or more intervening layers 410 are disposedbetween carrier layer 405 and device layer 415. In some exemplaryembodiments, an intervening layer 410 is compositionally distinct fromcarrier layer 405 such that it may serve as a marker detectable duringsubsequent removal of carrier layer 405. In some such embodiments, anintervening layer 410 has a composition that, when exposed to an etchantof carrier layer 405 will etch at a significantly slower rate thancarrier layer 405 (i.e., intervening layer 410 functions as an etch stopfor a carrier layer etch process). In further embodiments, interveninglayer 410 has a composition distinct from that of device layer 415.Intervening layer 410 may be a metal, semiconductor, or dielectricmaterial, for example.

In some exemplary embodiments where at least one of carrier layer 405and device layer 415 are crystalline semiconductors, intervening layer410 is also a crystalline semiconductor layer. Intervening layer 410 mayfurther have the same crystallinity and crystallographic orientation ascarrier layer 405 and/or device layer 415. Such embodiments may have theadvantage of reduced donor substrate cost relative to alternativeembodiments where intervening layer 410 is a material that necessitatesbonding (e.g., thermal-compression bonding) of intervening layer 410 tointervening layer 410 and/or to carrier layer 405.

For embodiments where intervening layer 410 is a semiconductor, one ormore of the primary semiconductor lattice elements, alloy constituents,or impurity concentrations may vary between at least carrier layer 405and intervening layer 410. In some embodiments where at least carrierlayer 405 is a group IV semiconductor, intervening layer 410 may also bea group IV semiconductor, but of a different group IV element or alloyand/or doped with an impurity species to an impurity level differentthan that of carrier layer 405. For example, intervening layer 410 maybe a silicon-germanium alloy epitaxially grown on a silicon carrier. Forsuch embodiments, a pseudomorphic intervening layer may be grownheteroepitaxially to any thickness below the critical thickness.Alternatively, the intervening layer 410 may be a relaxed buffer layerhaving a thickness greater than the critical thickness.

In other embodiments, where at least carrier layer 405 is a group III-Vsemiconductor, intervening layer 410 may also be a group III-Vsemiconductor, but of a different group III-V alloy and/or doped with animpurity species to an impurity level different than that of carrierlayer 405. For example, intervening layer 410 may be an AlGaAs alloyepitaxially grown on a GaAs carrier. In some other embodiments whereboth carrier layer 405 and device layer 415 are crystallinesemiconductors, intervening layer 410 is also a crystallinesemiconductor layer, which may further have the same crystallinity andcrystallographic orientation as carrier layer 405 and/or device layer415.

In embodiments where both carrier layer 405 and intervening layer 410are of the same or different primary semiconductor lattice elements,impurity dopants may differentiate the carrier and intervening layer.For example, intervening layer 410 and carrier layer 405 may both besilicon crystals with intervening layer 410 lacking an impurity presentin carrier layer 405, or doped with an impurity absent from carrierlayer 405, or doped to a different level with an impurity present incarrier layer 405. The impurity differentiation may impart etchselectivity between the carrier and intervening layer, or merelyintroduce a detectable species.

Intervening layer 410 may be doped with impurities that are electricallyactive (i.e., rendering it an n-type or p-type semiconductor), or not,as the impurity may provide any basis for detection of the interveninglayer 410 during subsequent carrier removal. Exemplary electricallyactive impurities for some semiconductor materials include group IIIelements (e.g., B), group IV elements (e.g., P). Any other element maybe employed as a non-electrically active species. Impurity dopantconcentration within intervening layer 410 need only vary from that ofcarrier layer 405 by an amount sufficient for detection, which may bepredetermined as a function of the detection technique and detectorsensitivity.

As described further elsewhere herein, intervening layer 410 may have acomposition distinct from device layer 415. In some such embodiments,intervening layer 410 may have a different band gap than that of devicelayer 415. For example, intervening layer 410 may have a wider band-gapthan device layer 415.

In embodiments where intervening layer 410 includes a dielectricmaterial, the dielectric material may be an inorganic material (e.g.,SiO, SiN, SiON, SiOC, hydrogen silsesquioxane, methyl silsesquioxane) ororganic material (polyimide, polynorbornenes, benzocyclobutene). Forsome dielectric embodiments, intervening layer 410 may be formed as anembedded layer (e.g., SiOx through implantation of oxygen into a silicondevice and/or carrier layer). Other embodiments of a dielectricintervening layer may necessitate bonding (e.g., thermal-compressionbonding) of carrier layer 405 to device layer 415. For example, wheredonor substrate 401 is a semiconductor-on-oxide (SOI) substrate, eitheror both of carrier layer 405 and device layer 415 may be oxidized andbonded together to form a SiO intervening layer 410. Similar bondingtechniques may be employed for other inorganic or organic dielectricmaterials.

In some other embodiments, intervening layer 410 includes two or morematerials laterally spaced apart within the layer. The two or morematerials may include a dielectric and a semiconductor, a dielectric anda metal, a semiconductor and a metal, a dielectric and a metal, twodifferent dielectric, two different semiconductors, or two differentmetals. Within such an intervening layer, a first material may surroundislands of the second material that extend through the thickness of theintervening layer. For example, an intervening layer may include a fieldisolation dielectric that surrounds islands of semiconductor, whichextend through the thickness of the intervening layer. The semiconductormay be epitaxially grown within openings of a patterned dielectric orthe dielectric material may be deposited within openings of a patternedsemiconductor.

In some exemplary embodiments, semiconductor features, such as fins ormesas, are etched into a front-side surface of a semiconductor devicelayer. Trenches surrounding these features may be subsequentlybackfilled with an isolation dielectric, for example following any knownshallow trench isolation (STI) process. One or more of the semiconductorfeature or isolation dielectric may be employed for terminating aback-side carrier removal process, for example as a back-side revealetch stop. In some embodiments, a reveal of trench isolation dielectricmay stop, significantly retard, or induce a detectable signal forterminating a back-side carrier polish. For example, a CMP polish ofcarrier semiconductor employing a slurry that has high selectivityfavoring removal of carrier semiconductor (e.g., Si) over removal ofisolation dielectric (e.g., SiO) may be significantly slowed uponexposure of a (bottom) surface of the trench isolation dielectricsurrounding semiconductor features including the device layer. Becausethe device layer is disposed on a front side of intervening layer, thedevice layer need not be directly exposed to the back-side revealprocess.

Notably, for embodiments where the intervening layer includes bothsemiconductor and dielectric, the intervening layer thickness may beconsiderably greater than the critical thickness associated with thelattice mismatch of the intervening layer and carrier. Whereas anintervening layer below critical thickness may be an insufficientthickness to accommodate non-uniformity of a wafer-level back-sidereveal process, embodiments with greater thickness may advantageouslyincrease the back-side reveal process window. Embodiments with pin-holeddielectric may otherwise facilitate subsequent separation of carrier anddevice layers as well as improve crystal quality within the devicelayer.

Semiconductor material within intervening layers that include bothsemiconductor and dielectric may also be homoepitaxial. In someexemplary embodiments, a silicon epitaxial device layer is grown througha pin-holed dielectric disposed over a silicon carrier layer.

Continuing with description of FIGS. 4A and 5A, intervening layer 410may also be a metal. For such embodiments, the metal may be of anycomposition known to be suitable for bonding to carrier layer 405 ordevice layer 415. For example, either or both of carrier layer 405 anddevice layer 415 may be finished with a metal, such as, but not limitedto Au or Pt, and subsequently bonded together, for example to form an Auor Pt intervening layer 410. Such a metal may also be part of anintervening layer that further includes a patterned dielectricsurrounding metal features.

Intervening layer 410 may be of any thickness (e.g., z-height in FIG.5A). The intervening layer should be sufficiently thick to ensure thecarrier removal operation can be reliably terminated before exposingdevice regions and/or device layer 415. Exemplary thicknesses forintervening layer 410 range from a few hundred nanometers to a fewmicrometers and may vary as a function of the amount of carrier materialthat is to be removed, the uniformity of the carrier removal process,and the selectivity of the carrier removal process, for example. Forembodiments where the intervening layer has the same crystallinity andcrystallographic orientation as carrier layer 405, the carrier layerthickness may be reduced by the thickness of intervening layer 410. Inother words, intervening layer 410 may be a top portion of a 700-1000 μmthick group IV crystalline semiconductor substrate also employed as thecarrier layer. In pseudomorphic heteroepitaxial embodiments, interveninglayer thickness may be limited to the critical thickness. Forheteroepitaxial intervening layer embodiments employing aspect ratiotrapping (ART) or another fully relaxed buffer architecture, theintervening layer may have any thickness.

As further illustrated in FIGS. 4B and 5B, donor substrate 401 may bejoined to a host substrate 402 to form a donor-host substrate assembly403. In some exemplary embodiments, a front-side surface of donorsubstrate 401 is joined to a surface of host substrate 402 such thatdevice layer 415 is proximal host substrate 402 and carrier layer 405 isdistal from host substrate 402. Host substrate 402 may be any substrateknown to be suitable for joining to device layer 415 and/or a front-sidestack fabricated over device layer 415. In some embodiments, hostsubstrate 402 includes one or more additional device strata. Forexample, host substrate 402 may further include one or more device layer(not depicted). Host substrate 402 may include integrated circuitry withwhich the IC devices fabricated in a device layer of host substrate 402are interconnected, in which case joining of device layer 415 to hostsubstrate 402 may further entail formation of 3D interconnect structuresthrough the wafer-level bond.

Although not depicted in detail by FIG. 5B, any number of front-sidelayers, such as interconnect metallization levels and interlayerdielectric (ILD) layers, may be present between device layer 415 andhost substrate 402. Any technique may be employed to join host substrate402 and donor substrate 401. In some exemplary embodiments furtherdescribed elsewhere herein, the joining of donor substrate 401 to hostsubstrate 402 is through metal-metal, oxide-oxide, or hybrid(metal/oxide-metal/oxide) thermal compression bonding.

With host substrate 402 facing device layer 415 on a side oppositecarrier layer 405, at least a portion of carrier layer 405 may beremoved as further illustrated in FIGS. 4C and 5C. Where the entirecarrier layer 405 is removed, donor-host substrate assembly 403maintains a highly uniform thickness with planar back side and frontside surfaces. Alternatively, carrier layer 405 may be masked andintervening layer 410 exposed only in unmasked sub-regions to form anon-planar back side surface. In the exemplary embodiments illustratedby FIGS. 4C and 5C, carrier layer 405 is removed from the entireback-side surface of donor-host substrate assembly 403. Carrier layer405 may be removed, for example by cleaving, grinding, and/or polishing(e.g., chemical-mechanical polishing), and/or wet chemical etching,and/or plasma etching through a thickness of the carrier layer to exposeintervening layer 410. One or more operations may be employed to removecarrier layer 405. Advantageously, the removal operation(s) may beterminated based on duration or an endpoint signal sensitive to exposureof intervening layer 410.

In further embodiments, for example as illustrated by FIGS. 4D and 5D,intervening layer 410 is also at least partially etched to expose a backside of device layer 415. At least a portion of intervening layer 410may be removed subsequent to its use as a carrier layer etch stop and/orcarrier layer etch endpoint trigger. Where the entire intervening layer410 is removed, donor-host substrate assembly 403 maintains a highlyuniform device layer thickness with planar back-side and front-sidesurfaces afforded by the intervening layer being much thinner than thecarrier layer. Alternatively, intervening layer 410 may be masked anddevice layer 415 exposed only in unmasked sub-regions, thereby forming anon-planar back-side surface. In the exemplary embodiments illustratedby FIGS. 4D and 5D, intervening layer 410 is removed from the entireback-side surface of donor-host substrate assembly 403. Interveninglayer 410 may be so removed, for example, by polishing (e.g.,chemical-mechanical polishing), and/or blanket wet chemical etching,and/or blanket plasma etching through a thickness of the interveninglayer to expose device layer 415. One or more operations may be employedto remove intervening layer 410. Advantageously, the removaloperation(s) may be terminated based on duration or an endpoint signalsensitive to exposure of device layer 415.

In some further embodiments, for example as illustrated by FIGS. 4E and5E, device layer 415 is partially etched to expose a back side of adevice structure previously formed from during front-side processing. Atleast a portion of device layer 415 may be removed subsequent to its usein fabricating one or more of the device semiconductor regions, and/orits use as an intervening layer etch stop or endpoint trigger. Wheredevice layer 415 is thinned over the entire substrate area, donor-hostsubstrate assembly 403 maintains a highly uniform reduced thickness withplanar back and front surfaces. Alternatively, device layer 415 may bemasked and device structures (e.g., device semiconductor regions)selectively revealed only in unmasked sub-regions, thereby forming anon-planar back-side surface. In the exemplary embodiments illustratedby FIGS. 4E and 5E, device layer 415 is thinned over the entireback-side surface of donor-host substrate assembly 403. Device layer 415may be thinned, for example by polishing (e.g., chemical-mechanicalpolishing), and/or wet chemical etching, and/or plasma etching through athickness of the device layer to expose one or more device semiconductorregions, and/or one or more other device structures (e.g., front-sidedevice terminal contact metallization, spacer dielectric, etc.)previously formed during front-side processing. One or more operationsmay be employed to thin device layer 415. Advantageously, the devicelayer thinning may be terminated based on duration or an endpoint signalsensitive to exposure of patterned features within device layer 415. Forexample, where front-side processing forms device isolation features(e.g., shallow trench isolation), back-side thinning of device layer 415may be terminated upon exposing the isolation dielectric material.

A non-native material layer may be deposited over a back-side surface ofan intervening layer, device layer, and/or specific device regionswithin device layer 415, and/or over or more other device structures(e.g., front-side device terminal contact metallization, spacerdielectric, etc.). One or more materials exposed (revealed) from thebackside may be covered with non-native material layer or replaced withsuch a material. In some embodiments, illustrated by FIGS. 4F and 5F,non-native material layer 420 is deposited on device layer 415.Non-native material layer 420 may be any material having a compositionand/or microstructure distinct from that of the material removed toreveal the backside of the device stratum. For example, whereintervening layer 410 is removed to expose device layer 415, non-nativematerial layer 420 may be another semiconductor of different compositionor microstructure than that of intervening layer 410. In some suchembodiments where device layer 415 is a group III-N semiconductor,non-native material layer 420 may also be a group III-N semiconductor ofthe same or different composition that is regrown upon a revealedbackside surface of a group III-N device region. This material may beepitaxially regrown from the revealed group III-N device region, forexample, to have better crystal quality than that of the materialremoved, and/or to induce strain within the device layer and/or deviceregions within the device layer, and/or to form a vertical (e.g.,z-dimension) stack of device semiconductor regions suitable for astacked device.

In some other embodiments where device layer 415 is a group III-Vsemiconductor, non-native material layer 420 may also be a group III-Vsemiconductor of the same or different composition that is regrown upona revealed backside surface of a group III-V device region. Thismaterial may be epitaxially regrown from the revealed group III-V deviceregion, for example, to have relatively better crystal quality than thatof the material removed, and/or to induce strain within the device layeror a specific device region within the device layer, and/or to form avertical stack of device semiconductor regions suitable for a stackeddevice.

In some other embodiments where device layer 415 is a group IVsemiconductor, non-native material layer 420 may also be a group IVsemiconductor of the same or different composition that is regrown upona revealed backside surface of a group IV device region. This materialmay be epitaxially regrown from the revealed group IV device region, forexample, to have relatively better crystal quality than that of thematerial removed, and/or to induce strain within the device region,and/or to form a stack of device semiconductor regions suitable for astacked device.

In some other embodiments, non-native material layer 420 is a dielectricmaterial, such as, but not limited to SiO, SiON, SiOC, hydrogensilsesquioxane, methyl silsesquioxane, polyimide, polynorbornenes,benzocyclobutene, or the like. Deposition of such a dielectric may serveto electrically isolate various device structures, such as semiconductordevice regions, that may have been previously formed during front-sideprocessing of donor substrate 401.

In some other embodiments, non-native material layer 420 is a conductivematerial, such as any elemental metal or metal alloy known to besuitable for contacting one or more surfaces of device regions revealedfrom the backside. In some embodiments, non-native material layer 420 isa metallization suitable for contacting a device region revealed fromthe backside, such as a transistor source or drain region. Inembodiments, intermetallic contacts such as NixSiy, TixSiy, Ni:Si:Pt,TiSi, CoSi, etc. may be formed. Additionally, implants may be used toenable robust contacts (e.g., P, Ge, B etc.).

In some embodiments, non-native material layer 420 is a stack ofmaterials, such as a FET gate stack that includes both a gate dielectriclayer and a gate electrode layer. As one example, non-native materiallayer 420 may be a gate dielectric stack suitable for contacting asemiconductor device region revealed from the backside, such as atransistor channel region. Any of the other the materials described asoptions for device layer 415 may also be deposited over a backside ofdevice layer 415 and/or over device regions formed within device layer415. For example, non-native material layer 420 may be any of the oxidesemiconductors, TMDC, or tunneling materials described above, which maybe deposited on the back-side, for example, to incrementally fabricatevertically-stacked device strata.

Back-side wafer-level processing may continue in any manner known to besuitable for front-side processing. For example, non-native materiallayer 420 may be patterned into active device regions, device isolationregions, device contact metallization, or device interconnects using anyknown lithographic and etch techniques. Back-side wafer-level processingmay further fabricate one or more interconnect metallization levelscoupling terminals of different devices into an IC. In some embodimentsfurther described elsewhere herein, back-side processing may be employedto interconnect a power bus to various device terminals within an IC.

In some embodiments, back-side processing includes bonding to asecondary host substrate. Such bonding may employ any layer transferprocess to join the back-side (e.g., non-native) material layer toanother substrate. Following such joining, the former host substrate maybe removed as a sacrificial donor to re-expose the front-side stackand/or the front side of the device layer. Such embodiments may enableiterative side-to-side lamination of device strata with a first devicelayer serving as the core of the assembly. In some embodimentsillustrated in FIGS. 4G and 5G, secondary host substrate 440 joined tonon-native material layer 420 provides at least mechanical support whilehost substrate 402 is removed.

Any bonding, such as, but not limited to, thermal-compression bondingmay be employed to join secondary host substrate 440 to non-nativematerial layer 420. In some embodiments, both a surface layer ofsecondary host substrate 440 and non-native material layer 420 arecontinuous dielectric layers (e.g., SiO), which are thermal-compressionbonded. In some other embodiments, both a surface layer of secondaryhost substrate 440 and non-native material layer 420 include a metallayer (e.g., Au, Pt, etc.), which are thermal-compression bonded. Inother embodiments, at least one of surface layer of secondary hostsubstrate 440 and non-native material layer 420 are patterned, includingboth patterned metal surface (i.e., traces) and surrounding dielectric(e.g., isolation), which are thermal-compression bonded to form a hybrid(e.g., metal/oxide) joint. For such embodiments, structural features inthe secondary host substrate 440 and the patterned non-native materiallayer 420 are aligned (e.g., optically) during the bonding process. Insome embodiments, non-native material layer 420 includes one or moreconductive back-side traces coupled to a terminal of a transistorfabricated in device layer 415. The conductive back-side trace may, forexample, be bonded to metallization on secondary host substrate 440.

Bonding of device strata may proceed from the front-side and/orback-side of a device layer before or after front-side processing of thedevice layer has been completed. A back-side bonding process may beperformed after front-side fabrication of a device (e.g., transistor) issubstantially complete. Alternatively, back-side bonding process may beperformed prior to completing front-side fabrication of a device (e.g.,transistor), in which case the front side of the device layer mayreceive additional processing following the back-side bonding process.As further illustrated in FIGS. 4H and 5H, for example, front-sideprocessing includes removal of host substrate 402 (as a second donorsubstrate) to re-expose the front side of device layer 415. At thispoint, donor-host substrate assembly 403 includes secondary host 440joined to device layer 415 through non-native material layer 420.

In another aspect, the vertical diode structures described above inassociation with FIG. 2C can be co-integrated with other substrate-lessintegrated circuit structures such as neighboring semiconductorstructures or devices separated by self-aligned gate endcap (SAGE)structures. Alternatively, or additionally, substrate-less integratedcircuit structures separated by SAGE structures may be fabricated toinclude backside epitaxial semiconductor structures. Particularembodiments may be directed to integration of multiple width (multi-Wsi)nanowires and nanoribbons in a SAGE architecture and separated by a SAGEwall. In an embodiment, nanowires/nanoribbons are integrated withmultiple Wsi in a SAGE architecture portion of a front-end process flow.Such a process flow may involve integration of nanowires and nanoribbonsof different Wsi to provide robust functionality of next generationtransistors with low power and high performance. Associated epitaxialsource or drain regions may be embedded (e.g., portions of nanowiresremoved and then source or drain (S/D) growth is performed).

To provide further context, advantages of a self-aligned gate endcap(SAGE) architecture may include the enabling of higher layout densityand, in particular, scaling of diffusion to diffusion spacing. Toprovide illustrative comparison, FIG. 6 illustrates a cross-sectionalview taken through nanowires and fins for a non-endcap architecture, inaccordance with an embodiment of the present disclosure. FIG. 7illustrates a cross-sectional view taken through nanowires and fins fora self-aligned gate endcap (SAGE) architecture, in accordance with anembodiment of the present disclosure.

Referring to FIG. 6, an integrated circuit structure 600 includes asubstrate 602 having fins 604 protruding there from by an amount 606above an isolation structure 608 laterally surrounding lower portions ofthe fins 604. Upper portions of the fins may include a local isolationstructure 622 and a growth enhancement layer 620, as is depicted.Corresponding nanowires 605 are over the fins 604. A gate structure maybe formed over the integrated circuit structure 600 to fabricate adevice. However, breaks in such a gate structure may be accommodated forby increasing the spacing between fin 604/nanowire 605 pairs.

Referring to FIG. 6, in an embodiment, following gate formation, thelower portions of the structure 600 can be planarized and/or etched tolevel 634 in order to leave a backside surface including exposed bottomsurfaces of gate structures and epitaxial source or drain structures. Itis to be appreciated that backside (bottom) contacts may be formed onthe exposed bottom surfaces of the epitaxial source or drain structures.It is also to be appreciated that planarization and/or etching could beto other levels such as 630 or 632.

By contrast, referring to FIG. 7, an integrated circuit structure 750includes a substrate 752 having fins 754 protruding therefrom by anamount 756 above an isolation structure 758 laterally surrounding lowerportions of the fins 754. Upper portions of the fins may include a localisolation structure 772 and a growth enhancement layer 770, as isdepicted. Corresponding nanowires 755 are over the fins 754. IsolatingSAGE walls 760 (which may include a hardmask thereon, as depicted) areincluded within the isolation structure 758 and between adjacent fin754/nanowire 755 pairs. The distance between an isolating SAGE wall 760and a nearest fin 754/nanowire 755 pair defines the gate endcap spacing762. A gate structure may be formed over the integrated circuitstructure 750, between insolating SAGE walls to fabricate a device.Breaks in such a gate structure are imposed by the isolating SAGE walls.Since the isolating SAGE walls 760 are self-aligned, restrictions fromconventional approaches can be minimized to enable more aggressivediffusion to diffusion spacing. Furthermore, since gate structuresinclude breaks at all locations, individual gate structure portions maybe layer connected by local interconnects formed over the isolating SAGEwalls 760. In an embodiment, as depicted, the isolating SAGE walls 760each include a lower dielectric portion and a dielectric cap on thelower dielectric portion.

Referring to FIG. 7, in an embodiment, following gate formation, thelower portions of the structure 700 can be planarized and/or etched tolevel 784 in order to leave a backside surface including exposed bottomsurfaces of gate structures and epitaxial source or drain structures. Itis to be appreciated that backside (bottom) contacts may be formed onthe exposed bottom surfaces of the epitaxial source or drain structures.It is also to be appreciated that planarization and/or etching could beto other levels such as 780 or 782.

A self-aligned gate endcap (SAGE) processing scheme involves theformation of gate/trench contact endcaps self-aligned to fins withoutrequiring an extra length to account for mask mis-registration. Thus,embodiments may be implemented to enable shrinking of transistor layoutarea. Embodiments described herein may involve the fabrication of gateendcap isolation structures, which may also be referred to as gatewalls, isolation gate walls or self-aligned gate endcap (SAGE) walls.

In an embodiment, as described throughout, self-aligned gate endcap(SAGE) isolation structures may be composed of a material or materialssuitable to ultimately electrically isolate, or contribute to theisolation of, portions of permanent gate structures from one another.Exemplary materials or material combinations include a single materialstructure such as silicon dioxide, silicon oxy-nitride, silicon nitride,or carbon-doped silicon nitride. Other exemplary materials or materialcombinations include a multi-layer stack having lower portion silicondioxide, silicon oxy-nitride, silicon nitride, or carbon-doped siliconnitride and an upper portion higher dielectric constant material such ashafnium oxide.

It is to be appreciated that the vertical diode structures describedabove in association with FIG. 2C can be co-integrated with othersubstrate-less integrated circuit structures such as nanowire ornanoribbon based devices. Alternatively, or additionally, nanowire ornanoribbon based substrate-less integrated circuit structures may befabricated to include backside epitaxial semiconductor structures. As anexample of a substrate-less device for co-integration or for inclusionof backside epitaxial semiconductor structures, and to highlight anexemplary integrated circuit structure having three vertically arrangednanowires, FIG. 8A illustrates a three-dimensional cross-sectional viewof a nanowire-based integrated circuit structure, in accordance with anembodiment of the present disclosure. FIG. 8B illustrates across-sectional source or drain view of the nanowire-based integratedcircuit structure of FIG. 8A, as taken along an a-a′ axis. FIG. 8Cillustrates a cross-sectional channel view of the nanowire-basedintegrated circuit structure of FIG. 8A, as taken along the b-b′ axis.

Referring to FIG. 8A, an integrated circuit structure 800 includes oneor more vertically stacked nanowires (804 set) above a substrate 802. Inan embodiment, as depicted, a local isolation structure 802C, a growthenhancement layer 802B, and a lower substrate portion 802A are includedin substrate 802, as is depicted. An optional fin below the bottommostnanowire and formed from the substrate 802 is not depicted for the sakeof emphasizing the nanowire portion for illustrative purposes.Embodiments herein are targeted at both single wire devices and multiplewire devices. As an example, a three nanowire-based devices havingnanowires 804A, 804B and 804C is shown for illustrative purposes. Forconvenience of description, nanowire 804A is used as an example wheredescription is focused on one of the nanowires. It is to be appreciatedthat where attributes of one nanowire are described, embodiments basedon a plurality of nanowires may have the same or essentially the sameattributes for each of the nanowires.

Each of the nanowires 804 includes a channel region 806 in the nanowire.The channel region 806 has a length (L). Referring to FIG. 8C, thechannel region also has a perimeter (Pc) orthogonal to the length (L).Referring to both FIGS. 8A and 8C, a gate electrode stack 808 surroundsthe entire perimeter (Pc) of each of the channel regions 806. The gateelectrode stack 808 includes a gate electrode along with a gatedielectric layer between the channel region 806 and the gate electrode(not shown). In an embodiment, the channel region is discrete in that itis completely surrounded by the gate electrode stack 808 without anyintervening material such as underlying substrate material or overlyingchannel fabrication materials. Accordingly, in embodiments having aplurality of nanowires 804, the channel regions 806 of the nanowires arealso discrete relative to one another.

Referring to both FIGS. 8A and 8B, integrated circuit structure 800includes a pair of non-discrete source or drain regions 810/812. Thepair of non-discrete source or drain regions 810/812 is on either sideof the channel regions 806 of the plurality of vertically stackednanowires 804. Furthermore, the pair of non-discrete source or drainregions 810/812 is adjoining for the channel regions 806 of theplurality of vertically stacked nanowires 804. In one such embodiment,not depicted, the pair of non-discrete source or drain regions 810/812is directly vertically adjoining for the channel regions 806 in thatepitaxial growth is on and between nanowire portions extending beyondthe channel regions 806, where nanowire ends are shown within the sourceor drain structures. In another embodiment, as depicted in FIG. 8A, thepair of non-discrete source or drain regions 810/812 is indirectlyvertically adjoining for the channel regions 806 in that they are formedat the ends of the nanowires and not between the nanowires.

In an embodiment, as depicted, the source or drain regions 810/812 arenon-discrete in that there are not individual and discrete source ordrain regions for each channel region 806 of a nanowire 804.Accordingly, in embodiments having a plurality of nanowires 804, thesource or drain regions 810/812 of the nanowires are global or unifiedsource or drain regions as opposed to discrete for each nanowire. Thatis, the non-discrete source or drain regions 810/812 are global in thesense that a single unified feature is used as a source or drain regionfor a plurality (in this case, 3) of nanowires 804 and, moreparticularly, for more than one discrete channel region 806. In oneembodiment, from a cross-sectional perspective orthogonal to the lengthof the discrete channel regions 806, each of the pair of non-discretesource or drain regions 810/812 is approximately rectangular in shapewith a bottom tapered portion and a top vertex portion, as depicted inFIG. 8B. In other embodiments, however, the source or drain regions810/812 of the nanowires are relatively larger yet discretenon-vertically merged epitaxial structures such as nubs.

In accordance with an embodiment of the present disclosure, and asdepicted in FIGS. 8A and 8B, integrated circuit structure 800 furtherincludes a pair of contacts 814, each contact 814 on one of the pair ofnon-discrete source or drain regions 810/812. In one such embodiment, ina vertical sense, each contact 814 completely surrounds the respectivenon-discrete source or drain region 810/812. In another aspect, theentire perimeter of the non-discrete source or drain regions 810/812 maynot be accessible for contact with contacts 814, and the contact 814thus only partially surrounds the non-discrete source or drain regions810/812, as depicted in FIG. 8B. In a contrasting embodiment, notdepicted, the entire perimeter of the non-discrete source or drainregions 810/812, as taken along the a-a′ axis, is surrounded by thecontacts 814.

Referring again to FIG. 8A, in an embodiment, integrated circuitstructure 800 further includes a pair of spacers 816. As is depicted,outer portions of the pair of spacers 816 may overlap portions of thenon-discrete source or drain regions 810/812, providing for “embedded”portions of the non-discrete source or drain regions 810/812 beneath thepair of spacers 816. As is also depicted, the embedded portions of thenon-discrete source or drain regions 810/812 may not extend beneath theentirety of the pair of spacers 816.

Substrate 802 may be composed of a material suitable for integratedcircuit structure fabrication. In one embodiment, substrate 802 includesa lower bulk substrate composed of a single crystal of a material whichmay include, but is not limited to, silicon, germanium,silicon-germanium, germanium-tin, silicon-germanium-tin, or a groupIII-V compound semiconductor material. An upper insulator layer composedof a material which may include, but is not limited to, silicon dioxide,silicon nitride or silicon oxy-nitride is on the lower bulk substrate.Thus, the structure 800 may be fabricated from a startingsemiconductor-on-insulator substrate. Alternatively, the structure 800is formed directly from a bulk substrate and local oxidation is used toform electrically insulative portions in place of the above describedupper insulator layer. In another alternative embodiment, the structure800 is formed directly from a bulk substrate and doping is used to formelectrically isolated active regions, such as nanowires, thereon. In onesuch embodiment, the first nanowire (i.e., proximate the substrate) isin the form of an omega-FET type structure.

In an embodiment, the nanowires 804 may be sized as wires or ribbons, asdescribed below, and may have squared-off or rounder corners. In anembodiment, the nanowires 804 are composed of a material such as, butnot limited to, silicon, germanium, or a combination thereof. In onesuch embodiment, the nanowires are single-crystalline. For example, fora silicon nanowire 804, a single-crystalline nanowire may be based froma (100) global orientation, e.g., with a <100> plane in the z-direction.As described below, other orientations may also be considered. In anembodiment, the dimensions of the nanowires 804, from a cross-sectionalperspective, are on the nano-scale. For example, in a specificembodiment, the smallest dimension of the nanowires 804 is less thanapproximately 20 nanometers. In an embodiment, the nanowires 804 arecomposed of a strained material, particularly in the channel regions806.

Referring to FIG. 8C, in an embodiment, each of the channel regions 806has a width (Wc) and a height (Hc), the width (Wc) approximately thesame as the height (Hc). That is, in both cases, the channel regions 806are square-like or, if corner-rounded, circle-like in cross-sectionprofile. In another aspect, the width and height of the channel regionneed not be the same, such as the case for nanoribbons as describedthroughout.

Referring again to FIGS. 8A, 8B and 8C, in an embodiment, the lowerportions of the structure 800 can be planarized and/or etched to level899 in order to leave a backside surface including exposed bottomsurfaces of gate structures and epitaxial source or drain structures. Itis to be appreciated that backside (bottom) contacts may be formed onthe exposed bottom surfaces of the epitaxial source or drain structures.

In an embodiment, as described throughout, an integrated circuitstructure includes non-planar devices such as, but not limited to, afinFET or a tri-gate structure with corresponding one or more overlyingnanowire structures, and an isolation structure between the finFET ortri-gate structure and the corresponding one or more overlying nanowirestructures. In some embodiments, the finFET or tri-gate structure isretained. In other embodiments, the finFET or tri-gate structure is mayultimately be removed in a substrate removal process.

Embodiments disclosed herein may be used to manufacture a wide varietyof different types of integrated circuits and/or microelectronicdevices. Examples of such integrated circuits include, but are notlimited to, processors, chipset components, graphics processors, digitalsignal processors, micro-controllers, and the like. In otherembodiments, semiconductor memory may be manufactured. Moreover, theintegrated circuits or other microelectronic devices may be used in awide variety of electronic devices known in the arts. For example, incomputer systems (e.g., desktop, laptop, server), cellular phones,personal electronics, etc. The integrated circuits may be coupled with abus and other components in the systems. For example, a processor may becoupled by one or more buses to a memory, a chipset, etc. Each of theprocessor, the memory, and the chipset, may potentially be manufacturedusing the approaches disclosed herein.

FIG. 9 illustrates a computing device 900 in accordance with oneimplementation of an embodiment of the present disclosure. The computingdevice 900 houses a board 902. The board 902 may include a number ofcomponents, including but not limited to a processor 904 and at leastone communication chip 906. The processor 904 is physically andelectrically coupled to the board 902. In some implementations the atleast one communication chip 906 is also physically and electricallycoupled to the board 902. In further implementations, the communicationchip 906 is part of the processor 904.

Depending on its applications, computing device 900 may include othercomponents that may or may not be physically and electrically coupled tothe board 902. These other components include, but are not limited to,volatile memory (e.g., DRAM), non-volatile memory (e.g., ROM), flashmemory, a graphics processor, a digital signal processor, a cryptoprocessor, a chipset, an antenna, a display, a touchscreen display, atouchscreen controller, a battery, an audio codec, a video codec, apower amplifier, a global positioning system (GPS) device, a compass, anaccelerometer, a gyroscope, a speaker, a camera, and a mass storagedevice (such as hard disk drive, compact disk (CD), digital versatiledisk (DVD), and so forth).

The communication chip 906 enables wireless communications for thetransfer of data to and from the computing device 900. The term“wireless” and its derivatives may be used to describe circuits,devices, systems, methods, techniques, communications channels, etc.,that may communicate data through the use of modulated electromagneticradiation through a non-solid medium. The term does not imply that theassociated devices do not contain any wires, although in someembodiments they might not. The communication chip 906 may implement anyof a number of wireless standards or protocols, including but notlimited to Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16 family), IEEE802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE,GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, derivatives thereof, as well asany other wireless protocols that are designated as 3G, 4G, 5G, andbeyond. The computing device 900 may include a plurality ofcommunication chips 906. For instance, a first communication chip 906may be dedicated to shorter range wireless communications such as Wi-Fiand Bluetooth and a second communication chip 906 may be dedicated tolonger range wireless communications such as GPS, EDGE, GPRS, CDMA,WiMAX, LTE, Ev-DO, and others.

The processor 904 of the computing device 900 includes an integratedcircuit die packaged within the processor 904. The integrated circuitdie of the processor 904 may include one or more structures, such assubstrate-less integrated circuit structures, built in accordance withimplementations of embodiments of the present disclosure. The term“processor” may refer to any device or portion of a device thatprocesses electronic data from registers and/or memory to transform thatelectronic data into other electronic data that may be stored inregisters and/or memory.

The communication chip 906 also includes an integrated circuit diepackaged within the communication chip 906. The integrated circuit dieof the communication chip 906 may include one or more structures, suchas substrate-less integrated circuit structures, built in accordancewith implementations of embodiments of the present disclosure.

In further implementations, another component housed within thecomputing device 900 may contain an integrated circuit die that includesone or structures, such as substrate-less integrated circuit structures,built in accordance with implementations of embodiments of the presentdisclosure.

In various implementations, the computing device 900 may be a laptop, anetbook, a notebook, an ultrabook, a smartphone, a tablet, a personaldigital assistant (PDA), an ultra mobile PC, a mobile phone, a desktopcomputer, a server, a printer, a scanner, a monitor, a set-top box, anentertainment control unit, a digital camera, a portable music player,or a digital video recorder. In further implementations, the computingdevice 900 may be any other electronic device that processes data.

FIG. 10 illustrates an interposer 1000 that includes one or moreembodiments of the present disclosure. The interposer 1000 is anintervening substrate used to bridge a first substrate 1002 to a secondsubstrate 1004. The first substrate 1002 may be, for instance, anintegrated circuit die. The second substrate 1004 may be, for instance,a memory module, a computer motherboard, or another integrated circuitdie. Generally, the purpose of an interposer 1000 is to spread aconnection to a wider pitch or to reroute a connection to a differentconnection. For example, an interposer 1000 may couple an integratedcircuit die to a ball grid array (BGA) 1006 that can subsequently becoupled to the second substrate 1004. In some embodiments, the first andsecond substrates 1002/1004 are attached to opposing sides of theinterposer 1000. In other embodiments, the first and second substrates1002/1004 are attached to the same side of the interposer 1000. And infurther embodiments, three or more substrates are interconnected by wayof the interposer 1000.

The interposer 1000 may be formed of an epoxy resin, afiberglass-reinforced epoxy resin, a ceramic material, or a polymermaterial such as polyimide. In further implementations, the interposer1000 may be formed of alternate rigid or flexible materials that mayinclude the same materials described above for use in a semiconductorsubstrate, such as silicon, germanium, and other group III-V and groupIV materials.

The interposer 1000 may include metal interconnects 1008 and vias 1010,including but not limited to through-silicon vias (TSVs) 1012. Theinterposer 1000 may further include embedded devices 1014, includingboth passive and active devices. Such devices include, but are notlimited to, capacitors, decoupling capacitors, resistors, inductors,fuses, diodes, transformers, sensors, and electrostatic discharge (ESD)devices. More complex devices such as radio-frequency (RF) devices,power amplifiers, power management devices, antennas, arrays, sensors,and MEMS devices may also be formed on the interposer 1000. Inaccordance with embodiments of the disclosure, apparatuses or processesdisclosed herein may be used in the fabrication of interposer 1000 or inthe fabrication of components included in the interposer 1000.

Thus, embodiments of the present disclosure include substrate-lessvertical diode integrated circuit structures, and methods of fabricatingsubstrate-less vertical diode integrated circuit structures.

The above description of illustrated implementations of embodiments ofthe disclosure, including what is described in the Abstract, is notintended to be exhaustive or to limit the disclosure to the preciseforms disclosed. While specific implementations of, and examples for,the disclosure are described herein for illustrative purposes, variousequivalent modifications are possible within the scope of thedisclosure, as those skilled in the relevant art will recognize.

These modifications may be made to the disclosure in light of the abovedetailed description. The terms used in the following claims should notbe construed to limit the disclosure to the specific implementationsdisclosed in the specification and the claims. Rather, the scope of thedisclosure is to be determined entirely by the following claims, whichare to be construed in accordance with established doctrines of claiminterpretation.

Example embodiment 1: A substrate-less integrated circuit structureincludes a semiconductor fin in a dielectric layer, the semiconductorfin having a top and a bottom, and the dielectric layer having a topsurface and a bottom surface. A first epitaxial semiconductor structureis on the top of the semiconductor fin. A second epitaxial semiconductorstructure is on the bottom of the semiconductor fin. A first conductivecontact is on the first epitaxial semiconductor structure. A secondconductive contact is on the second epitaxial semiconductor structure.

Example embodiment 2: The substrate-less integrated circuit structure ofexample embodiment 1, wherein the first epitaxial semiconductorstructure has a bottom below the top surface of the dielectric layer,and wherein the second epitaxial semiconductor structure has a top abovethe bottom surface of the dielectric layer.

Example embodiment 3: The substrate-less integrated circuit structure ofexample embodiment 1 or 2, wherein the fin includes silicon, and thefirst and second epitaxial semiconductor structures include silicon andgermanium.

Example embodiment 4: The substrate-less integrated circuit structure ofexample embodiment 1, 2 or 3, wherein the first and second epitaxialsemiconductor structures are faceted.

Example embodiment 5: The substrate-less integrated circuit structure ofexample embodiment 1, 2, 3 or 4, wherein the integrated circuitstructure is a vertical diode.

Example embodiment 6: A computing device includes a board, and acomponent coupled to the board. The component includes a substrate-lessintegrated circuit structure including a semiconductor fin in adielectric layer, the semiconductor fin having a top and a bottom, andthe dielectric layer having a top surface and a bottom surface. A firstepitaxial semiconductor structure is on the top of the semiconductorfin. A second epitaxial semiconductor structure is on the bottom of thesemiconductor fin. A first conductive contact is on the first epitaxialsemiconductor structure. A second conductive contact is on the secondepitaxial semiconductor structure.

Example embodiment 7: The computing device of example embodiment 6,further including a memory coupled to the board.

Example embodiment 8: The computing device of example embodiment 6 or 7,further including a communication chip coupled to the board.

Example embodiment 9: The computing device of example embodiment 6, 7 or8, wherein the component is a packaged integrated circuit die.

Example embodiment 10: The computing device of example embodiment 6, 7,8 or 9, wherein the component is selected from the group consisting of aprocessor, a communications chip, and a digital signal processor.

Example embodiment 11: A substrate-less integrated circuit structureincludes a plurality of fins in a dielectric layer. A plurality ofN-type epitaxial structures is on a top of the plurality of fins. Aplurality of P-type epitaxial structures is on a bottom of the pluralityof fins. A first conductive contact is on the plurality of N-typeepitaxial structures. A second conductive contact is on the plurality ofP-type epitaxial structures.

Example embodiment 12: The substrate-less integrated circuit structureof example embodiment 11, wherein the plurality of fins is a pluralityof N-type fins.

Example embodiment 13: The substrate-less integrated circuit structureof example embodiment 11, wherein the plurality of fins is a pluralityof P-type fins.

Example embodiment 14: The substrate-less integrated circuit structureof example embodiment 11, 12 or 13, wherein the plurality of finsincludes silicon, the plurality of N-type epitaxial structures includessilicon and germanium, and the plurality of P-type epitaxial structuresincludes silicon and germanium.

Example embodiment 15: The substrate-less integrated circuit structureof example embodiment 11, 12, 13 or 14, wherein the integrated circuitstructure is a vertical diode.

Example embodiment 16: A computing device includes a board, and acomponent coupled to the board. The component includes a substrate-lessintegrated circuit structure including a plurality of fins in adielectric layer. A plurality of N-type epitaxial structures is on a topof the plurality of fins. A plurality of P-type epitaxial structures ison a bottom of the plurality of fins. A first conductive contact is onthe plurality of N-type epitaxial structures. A second conductivecontact is on the plurality of P-type epitaxial structures.

Example embodiment 17: The computing device of example embodiment 16,further including a memory coupled to the board.

Example embodiment 18: The computing device of example embodiment 16 or17, further including a communication chip coupled to the board.

Example embodiment 19: The computing device of example embodiment 16, 17or 18, wherein the component is a packaged integrated circuit die.

Example embodiment 20: The computing device of example embodiment 6, 17,18 or 19, wherein the component is selected from the group consisting ofa processor, a communications chip, and a digital signal processor.

What is claimed is:
 1. A substrate-less integrated circuit structure,comprising: a semiconductor fin in a dielectric layer, the semiconductorfin having a top and a bottom, and the dielectric layer having a topsurface and a bottom surface; a first epitaxial semiconductor structureon the top of the semiconductor fin; a second epitaxial semiconductorstructure on the bottom of the semiconductor fin; a first conductivecontact on the first epitaxial semiconductor structure; and a secondconductive contact on the second epitaxial semiconductor structure. 2.The substrate-less integrated circuit structure of claim 1, wherein thefirst epitaxial semiconductor structure has a bottom below the topsurface of the dielectric layer, and wherein the second epitaxialsemiconductor structure has a top above the bottom surface of thedielectric layer.
 3. The substrate-less integrated circuit structure ofclaim 1, wherein the fin comprises silicon, and the first and secondepitaxial semiconductor structures comprise silicon and germanium. 4.The substrate-less integrated circuit structure of claim 1, wherein thefirst and second epitaxial semiconductor structures are faceted.
 5. Thesubstrate-less integrated circuit structure of claim 1, wherein theintegrated circuit structure is a vertical diode.
 6. A computing device,comprising: a board; and a component coupled to the board, the componentincluding a substrate-less integrated circuit structure, comprising: asemiconductor fin in a dielectric layer, the semiconductor fin having atop and a bottom, and the dielectric layer having a top surface and abottom surface; a first epitaxial semiconductor structure on the top ofthe semiconductor fin; a second epitaxial semiconductor structure on thebottom of the semiconductor fin; a first conductive contact on the firstepitaxial semiconductor structure; and a second conductive contact onthe second epitaxial semiconductor structure.
 7. The computing device ofclaim 6, further comprising: a memory coupled to the board.
 8. Thecomputing device of claim 6, further comprising: a communication chipcoupled to the board.
 9. The computing device of claim 6, wherein thecomponent is a packaged integrated circuit die.
 10. The computing deviceof claim 6, wherein the component is selected from the group consistingof a processor, a communications chip, and a digital signal processor.11. A substrate-less integrated circuit structure, comprising: aplurality of fins in a dielectric layer; a plurality of N-type epitaxialstructures on a top of the plurality of fins; a plurality of P-typeepitaxial structures on a bottom of the plurality of fins; a firstconductive contact on the plurality of N-type epitaxial structures; anda second conductive contact on the plurality of P-type epitaxialstructures.
 12. The substrate-less integrated circuit structure of claim11, wherein the plurality of fins is a plurality of N-type fins.
 13. Thesubstrate-less integrated circuit structure of claim 11, wherein theplurality of fins is a plurality of P-type fins.
 14. The substrate-lessintegrated circuit structure of claim 11, wherein the plurality of finscomprises silicon, the plurality of N-type epitaxial structurescomprises silicon and germanium, and the plurality of P-type epitaxialstructures comprises silicon and germanium.
 15. The substrate-lessintegrated circuit structure of claim 11, wherein the integrated circuitstructure is a vertical diode.
 16. A computing device, comprising: aboard; and a component coupled to the board, the component including asubstrate-less integrated circuit structure, comprising: a plurality offins in a dielectric layer; a plurality of N-type epitaxial structureson a top of the plurality of fins; a plurality of P-type epitaxialstructures on a bottom of the plurality of fins; a first conductivecontact on the plurality of N-type epitaxial structures; and a secondconductive contact on the plurality of P-type epitaxial structures. 17.The computing device of claim 16, further comprising: a memory coupledto the board.
 18. The computing device of claim 16, further comprising:a communication chip coupled to the board.
 19. The computing device ofclaim 16, wherein the component is a packaged integrated circuit die.20. The computing device of claim 16, wherein the component is selectedfrom the group consisting of a processor, a communications chip, and adigital signal processor.